Cl− can affect the H2S adsorption, consequently affecting hydrogen absorption and sulfide stress cracking. The objective of this study is to define H2S surface coverage (Equation) and use the developed (Equation) to evaluate the influences of NaCl on the H2S-accelerated hydrogen uptake and the cracking susceptibility of C110 in sour environments. The (Equation) description was defined using the inductance response (L) of EIS testing results. The positive correlation between hydrogen uptake fraction f and (Equation) was developed based on the hydrogen permeation results and electrochemical impedance spectroscopy results. A negative correlation between KIC and (Equation) was developed based on the notched tensile slow strain rate testing results at different H2S concentrations. This correlation was applied to predict KIC values in H2S environments with NaCl concentrations from 1 wt% to 20 wt%. The predicted and measured KIC values showed an opposite tendency as increasing NaCl concentrations. The measured KIC decreased with decreasing (Equation) resulting from increasing NaCl concentrations. The fracture surface study explained this inconsistence, which revealed that the increment in NaCl concentration increases the pitting density on the steel surface, which lowers the energy required for crack initiation and propagation.
The catastrophic failure of high-strength low-alloy (HSLA) carbon steel C110 pipelines can cause huge economic loss and environmental pollution. Most studies reported that sulfide stress cracking (SSC) is the principal failure type of C110 pipelines in sour environments 1-4. The mechanism of SSC can be described as follows: The adsorbed H2S on the steel surface can accelerate the hydrogen uptake by accelerating the hydrogen reduction reaction and catalyzing the hydrogen absorption process. The absorbed hydrogen atoms accumulate in the stress-concentrated region. If the hydrogen concentration in this region is higher than a critical value, the failure will occur even if the applied stress is much lower than the yield stress of steel due to the hydrogen embrittlement 5-7. To reduce the damage of SSC, it is necessary to find an efficient way to predict the susceptibility to SSC. Since SSC is a hydrogen-related cracking, the effects of environmental factors on hydrogen uptake have been interesting study topics for many researchers 3, 8-12.
